Propshafts are commonly employed for transmitting power from a rotational power source, such as the output shaft of a vehicle transmission, to a rotatably driven mechanism, such as a differential assembly. As is well known in the art, the torsional loading of the propshaft is rarely uniform over an extended period of time even at relatively constant vehicle speeds and as such, the propshaft is typically subjected to a continually varying torsional load. These variances in the torsional load carried by the propshaft tend to create torsional vibrations which may generate noise in the vehicle drivetrain or vehicle that is undesirable to passengers riding in the vehicle. In especially severe instances, the vibration that is transmitted through the propshaft can generate fatigue in the propshaft and other drivetrain components to thereby shorten the life of the vehicle drivetrain. Thus, it is desirable and advantageous to attenuate vibrations within the propshaft in order to reduce noise and guard against undue fatigue.
It is known in the art to provide tuned torsional vibrations dampers for attachment to shafts, such as crankshafts and propshafts, to attenuate torsional vibrations. This approach, however, has several drawbacks. One such drawback is that these devices are usually tuned to a specific frequency and consequently, will only damp vibrations within a relatively narrow frequency band. Accordingly, these devices are typically employed to effectively damp vibrations at a single critical frequency and offer little or no damping for vibrations which occur at other frequencies.
Another drawback with conventional mechanical damping devices relates to their incorporation into an application, such as an automotive vehicle. Generally speaking, these devices tend to have a relatively large mass, rendering their incorporation into a vehicle difficult due to their weight and overall size. Another concern is that it is frequently not possible to mount these devices in the position at which they would be most effective, as the size of the device will often not permit it to be packaged into the vehicle at a particular location.